yellowing of bottom marijuana leaves is common in flowering and sometimes happens to the bottom leaves in veg how ever the "brown" you report of leads me to belive you have a little over fert going on. espically since u said you used miracle grow. Mg is super concentraited and with out dilution a full feeding will most likely cause burning of the leaves, the brown will usually start at the tip of the leaves if it is over fert. depending on how much you over fed them leaves could turn entirely brown and drop off and if u give it way to much the whole plant could die. but its hard to say with out a picture. If you are talking about the very first set or two of leaves then i would say its normal and nothing to worry but if its anything higher then that and on a number of leaves i would say over fert. Gl and to be safe back off the MG :rastasmoke: